1. Field of the Invention
The present invention is directed generally to instruments for evaluating strength and, more specifically, to instruments for evaluating the strength of human fingers.
2. Description of the Background
Evaluation of the hands and the larger upper extremities, as currently performed in clinics and hospitals, consists of measurements of strength, range of motion, nerve sensation and graphic depiction of deformities of the hand, arm and shoulder. These measurements are required for pre-operative, post-operative, and periodic assessment of functional abnormality. To meet the requirements of most health and workman's compensation insurance, these measurements are standardized and reported in a consistent format throughout the United States. Evaluation techniques in other countries are quite similar, with expected changes in measurement units and reporting format.
The pinch meter is used to assess pinch strength. Pinch strength is important because it is one measure of the functionality of the fingers in conjunction with the opposed thumb. Because of its importance, three different measurements of pinch strength are usually taken: three point (thumb opposed by three fingers), four point (thumb opposed by four fingers), and key (thumb opposed laterally by all fingers as when holding a key). Pinch strength is measured in pounds or kilograms, and the typical range of value is from zero to thirty-five pounds.
Pinchmeters within the current state of the art are generally constructed of a metal beam having a "C" shaped cross-section. When a pinch force is applied to the top and bottom of the "C," the pinchmeter is deflected inward in proportion to the pinch strength applied. The deflection is measured by a dial indicator which is calibrated to read the pinch force exerted in either pounds or kilograms. The pinchmeter has an indicated surface for placing the thumb and fingers to obtain an accurate reading. Examples of this type pinch meter include the PC 5036M pinch gage manufactured by Therapeutic Equipment Corporation, 60 Page Road, Clifton, N.J. 07012, and the B&L Pinch Meter manufactured by North Coast Medical, Inc., 450 Salmar Avenue, Campbell, Calif. 95008. A variation of this type includes the PC 5030HPG hydraulic pinch gage manufactured under the Jamar.RTM. name by the J.A. Preston Corporation, 60 Page Road, Clifton, N.J. 07012.
Another type of pinchmeter recently introduced is the electronic pinchmeter. It has the electronics and force sensing technology to produce a digital reading of the pinch force applied. This type of pinchmeter typically uses a strain gage to measure deflection and converts that reading into a voltage which can be read by other devices, such as computers. These pinchmeters are constructed out of molded plastic and metal, and contain a circuit board with the electronic components necessary for the computer interface. An example of this type of pinch meter includes the PC 5030 PA digital pinch gage manufactured under the Jamar.RTM. name by the J.A. Preston Corporation.
Because of the importance of pinch strength to the functionality of the hand through the pinching movement of the fingers in relation to the thumb, and the importance of this measurement in evaluating impairment of the hand, it is imperative that measurement of pinch strength be accurate. Because the examiner can't determine whether a patient is or is not applying the maximum strength he is able to apply at the time of the examination, there is a need for a pinch meter with respect to which a patient is unable to accurately sense and then repeat application of a submaximal amount of pinch force. If a patient can accurately sense the measurement being taken, as by sensing the amount of movement of the component parts of the pinchmeter or by other sensory feedback, his ability to repeatedly apply a submaximal pinch force and to therefore "cheat" or "fake" the measurement is enhanced. There is also a need for a pinch meter that is shaped in a way that will allow the patient to easily place the fingers and thumb so as to accommodate all three of the primary pinch measurements and which will likewise avoid inaccuracies induced by minor misalignment of the thumb and fingers on the device itself.